Voltage notches are defined by IEEE 1195-1995 Standard, which states that a notch is “A switching (or other) disturbance of the normal power voltage waveform, lasting less than 0.5 cycles, which is initially of opposite polarity than the waveform and is thus subtracted from the normal waveform in terms of the peak value of the disturbance voltage. This includes complete loss of voltage for up to 0.5 cycles.” This standard categorizes notching as a type of waveform distortion as it occurs periodically and “is principally characterized by the spectral content of deviation.” As stated in IEEE 1195-1995, “the frequency components associated with notching can be quite high and may not be readily characterized with measurement equipment normally used for harmonic analysis.” Notching is generally caused by electrical power devices when current is commutated from one phase to another such as by sudden switching. During this period, there is a momentary short circuit between phases which results in the voltage notch. Notches primarily apply to switched loads such as those from adjustable speed drives. For example, when there is a sudden demand for voltage by a silicon-controlled rectifier (SCR) in an adjustable speed drive and a rapid draw on the overall voltage demand will be seen which typically shows up as a notch in the output waveform.
Thus, a notch can represent a steady-state power characteristic, which may occur on a normal sine wave signal. A normal sine wave electrical signal typically experiences two zero-axis crossings per cycle (henceforth referred to as zero-crossings). In some cases, these zero-crossings are a reference point for the control schemes of some equipment. Thus, severe notching may result in equipment misoperation, malfunction, lockups, and even equipment damage. Excess zero-crossings and/or deep voltage notches that do not cross the zero-axis may result in malfunction or misoperation of some equipment ultimately leading to premature equipment failures. For example, if a clock for a device depends on zero-crossing for timing, excess zero-crossings can cause malfunctions in the device operation.
Thus, detection of voltage notching in input signals is necessary to protect equipment that depends on accurate zero-crossings. Further, detection of voltage notching may be needed to protect equipment from malfunctions or damage. Existing systems do not allow for the efficient detection of voltage notching or the evaluation of voltage notching, which is necessary to diagnose and address the notching source.
What is needed, therefore, is a system to allow users to determine the occurrence of a voltage notch in an electrical system. There is also a need for a system to quantify the characteristics (including severity) of a voltage notch in an electrical system. There is a further need for a system and method to evaluate voltage notches and provide mitigation solutions. Aspects of the present invention are directed at addressing these and other needs.